A variety of methods exist for tracking and providing information about items. For example, inventory items typically carry printed labels providing information such as serial numbers, price, weight, and size. Some labels include data carriers in the form of machine-readable symbols that can be selected from a variety of machine-readable symbologies, such as bar code, and/or area or matrix code symbologies. The amount of information that the symbols can contain is limited by the space constraints of the label. Updating the information in these machine-readable symbols typically requires the printing of a new label to replace the old label.
Data carriers such as memory devices provide an alternative method for tracking and providing information about items. Memory devices permit the linking of large amounts of data with an object or item. Memory devices typically include a memory and logic in the form of an integrated circuit ("IC") and means for transmitting data to and/or from the device. For example, a radio frequency identification ("RFID") tag typically includes a memory for storing data, an antenna, an RF transmitter, and/or an RF receiver to transmit data, and logic for controlling the various components of the memory device. RFID tags are generally formed on a substrate and can include, for example, analog RF circuits and digital logic and memory circuits. The RFID tags can also include a number of discrete components, such as capacitors, transistors, and diodes.
RFID tags can be passive, active or hybrid devices. Active devices are self-powered, by a battery for example. Passive devices do not contain a discrete power source, but derive their energy from an RF signal used to interrogate the RFID tag. Passive RFID tags usually include an analog circuit that detects and decodes the interrogating RF signal and that provides power from the RF field to a digital circuit in the tag. The digital circuit generally executes all of the data functions of the RFID tag, such as retrieving stored data from memory and causing the analog circuit to modulate the RF signal to transmit the retrieved data. In addition to retrieving and transmitting data previously stored in the memory, the RFID tag can permit new or additional information to be stored in the RFID tag's memory, or can permit the RFID tag to manipulate data or perform some additional functions. RFID tags are available from a number of manufacturers, including Texas Instruments, Dallas, Texas, and Omron of Japan.
Another form of memory device is an optical tag. Optical tags are similar in many respects to RFID tags, but rely on an optical signal to transmit data to and/or from the tag.
Additionally, touch memory data carriers are available, for example touch memory devices from Dallas Semiconductor of Dallas, Texas. Touch memory devices are similar to RFID tags but require physical contact with to store and retrieve data.
A user typically secures a data carrier to an item, such as a good, product, or container by way of a pressure sensitive adhesive. The data carrier often encodes information specifically relating to the item such as identifying or destination information. An individual, such as a checkout or inventory clerk, can retrieve data about any given item, for example, by scanning the machine-readable symbol or interrogating the RF tag, optical tag, or touch memory device. Access to the data can be useful at the point of sale, during inventory, during transportation, or at other points in the manufacture, distribution, sale, or use of the tagged item.
Relatively high cost is one of the drawbacks of memory devices, thus, many applications rely on the less expensive printed machine-readable symbols. Another significant drawback is the difficulty of identifying a particular memory device from a group of memory devices. It is particularly difficult to associate the information read from the RFID tag with a physical item or container. The ability to read data from different types of data carriers, for example machine-readable symbols and RFID tags, and/or to associate and manipulate such data can provide numerous benefits in the automatic data collection ("ADC") industry.